Color photography



Patented Nov.' 2, 1943 COLOR PHOTOGRAPHY Albert L. Bunting, Detroit, Mich., assignor to Union Research Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application April 2'1, 1940, Serial No. 332,069

11 Claims.

The present invention relates to new and useful improvements in color photography relating more particularly to an improved method for producing a natural color print in a single emulsion layer and to an improved color print produced by said method.

It is well known in the art relating to color photography that one general method for producing a color print utilizes as an initial requisite a set of color separation negatives. Each of these negatives represents in terms of black-and-white a color in the scene photographed, more particularly the color of the filter through which it was exposed. In making a color photographic print from such a set of color separation negatives, an initial colored image is made which is given the color the said negative represents. One of these initial colored images is made for each color separation negative, and the plurality of such images is combined or assembled in registry to produce a completed colored print. The color value and intensity of each of these initial colored images must be carefully determined or the assembled images will not balance and form a natural appearing completed colored print. One method of producing each of the initial colored images depends upon the production of an initial black-and-whitepositive print exposed through a selected color separation negative. This initial black-and-white positive image is reproduced in terms of a desired color to form the colored image. Separate colored images thus formed are normally assembled by merely superimposing them in registry on a common base or carrier. However, the emulsion carrying each of these separate colored images may be transferred to a common base or carried and in some instances each separate colored image has been produced in one .of a plurality of emulsion layers initially disposed on the carrier.

However, to date no satisfactory method for producing a plurality of separate colored images in registry in a single emulsion layer has been devised. In particular no method has been devised which in a single emulsion layer produces each separate colored image from an initially produced black-and-white image because there has been no satisfactory method of forming a succession of black-and-white images in a single emulsion layer.

It is, therefore, a principal object of the present invention to provide an improved natural appearing color print and a process for producing the same in which a succession of satisfactory black-and-white images is produced in asingle emulsion layer each image being reproduced in terms of a desired color and being controlled as to color, intensity, gradation and definition and thereby adapted to provide a satisfactory completed natural color print when a plurality of these colored images is deposited in registry in a single emulsion layer.

Another object of the invention is to provide improved novel chemical toning or coloring means for converting an initial black-and-white image to an image of a desired color corresponding to the initial black-and-white image in intensity, definition and detail; and to provide image coloring means of this character for an initial black-and-white image and thereafter producing a successive black-and-White image in the same emulsion layer and which, in turn, is converted into another colored image and produces a desired number of difierently colored images in a single emulsion layer by continuing this general procedure.

It is another object of the invention to provide a novel improved colored photographic print in which a plurality of colored images is deposited in registry in a single emulsion layer each image having been exposed through one of a matched set of color representing negative and formed from an initial black-and-white image developed after such exposure; and to provide a process for producing a succession of black-andwhite images of a controlled intensity, definition and character satisfactory to be converted into said colored images.

It is a further object of the invention to provide in a process of the foregoing general character, a step or steps suited to convert a given black-and-white image into an intermediate reaction product image or converted image which is reactive with color forming agents while at the same time forming a light-sensitive deposit in the emulsion 0r forming an intermediate product readily converted into a light-sensitive material.

A further object of the invention is to provide a practical relatively simply produced and comparatively inexpensive photographic print hav ing a plurality of satisfactory photographic images of a. controlled intensity and character in a single emulsion layer, and in particular to provide in a single emulsion layer a plurality of differently colored images balanced and in registry to form a completed colored print, as well as to provide an improved novel process for producing colored prints of this nature which is comparatively simple, which is easily controlled, and in which a minimumnumber of prints is Production of color separation negatives 1 In carrying out the present invention a suitable set of color separation negatives is utilized as an initial requisite. Color separation negatives and suitable procedures for making them are well known in the art. However, colored processes heretofore have utilized color separation negatives which are flat, that is,'of relatively, little contrast and normally have also utilized light prints, that is, of relative low intensity. For purposes of the present invention color separation negatives should be of a relatively high contrast as well as relatively intense. A skilled photographer readily can make color separation negatives of this character and can select a suitable set of filters through which such negatives are exposed.

For present purposes, however, it is recommended that the filters known as Wratten A, B and C5 be employed. However, it is to be understood that any suitable set of filters, many of which are well known, may be utilized.

Color separation negatives particularly suited for production of color prints by the present method should be developed to an average intensity of approximately one gamma. This intensity control is achieved principally by a choice of developers and by development time in the development step and by control of exposure times.

After being developed and fixed the black-andwhite color separation negatives are washed and dried in the usual manner. They are then used for making black-and-white positive prints which in turn are used for the production of colored positive prints according to the present invention.

The production of an initial black-and-white image ing a single layer of emulsion produce satisfactory results, and in particular motion picture positive stock which possesses but a single coating of emulsion is recommended. Film such as manufacturers prepare for use in reversal processes normally possess these characteristics and are therefore suitable. However, any suitable film is contemplated. While, normally, such films are coated with a gelatin emulsion containing a light-sensitive silver salt such as silver bromide, it is to be understood that other lightsensitive materials also may be utilized. The black-and-white positive print is developed and fixed in suitable developing and fixing solutions which are well known in the art and conventional photographic technique and procedure are employed for this purpose. However, in pre- In preparing the black-and-white" positive prints it has been found that films havparing these biack-and-white positives the exposure time is important because, together with the nature of the color representing negative, it

, constitutes a principal control. means for the intensity of the black-and-white positive. density of this positive in turn is most important in determining the density of the colored image reproduced therefrom. Naturally, this exposure time will depend upon the character of the blackand-whlte color separationnegatives, the nature of the film employed to produce the positive,

the density of the ultimate color print desired,

the character of the developer, and other factors normally considered by photographers in printing any positive image. Preferably, this exposure time should be so determined that the black-and-white positive image will have a density of approximately .8 to 1 gamma on de-- again washed.

Bleaching the initial black-and -white image For the preparation of the colored images herein disclosed, the aforesaid black-and-white positive image is converted into an intermediate reaction product image. referred to in the art as bleaching." Any suitable bleaching agent may be employed such as chromic acid, chromates, halides, borates and the like, many of which are well known. However, the use of a solution of a ferricyanide, particularly potassium ferricyanide, is especially recommended as a bleaching agent. It is also recommended that the ferricyanide bleaching solution be buffered. Any suitable buffering agent may be employed, such as sodium bicarbonate, sodium acetate plus acetic acid, or the like. It will be appreciated that the blackandwhite image is normallya reduced metallic image. Therefore, any reagent reactive with the blackand-white image to form a water insoluble reaction product of the metal may be employed as the bleaching agent.

The bleached image is suitably washed to remove any excess of the bleaching solution which may remain in or on the image. For potassium ferricyanide a five minute wash in running water is recommended although suitable variations may, of course, be made to suit particular conditions.

Replacement of a metal of the bleached image with a chemically active metal; the "conversion operation The initial black-and-white image having been 'bleached is next placed in-a bath which 1 the metallic black-and-white image. The replacing metal must be above the replaced metal in the electromotive series in order to be operable.

The

This step is commonly.

, 2,333,259 -Usually the replaced metallic element of the bleached image is silver so that one of the metals above silver in the electromotive series may be employed, for example, a solution of a zinc salt. Suitable compounds of copper, aluminum, tin, nickel, and other equivalents for zinc may also be used. Of these metals, it has been found that zinc produces the most satisfactory results and therefore the use of a zinc compound is particularly recommended. While this reaction is correctly referred to as a replacement it may also be referred to as double decomposition and as metathesis. The bleached image after being reacted to have the metal element thereof initially forming the black-and-white image replaced by another metal is referred'to herein as the converted image.

Assuming that the initial black-ancl-white image was silver, that the bleaching agent was a ferricyanide, and that the replacing metal was zinc, the converted image is Zinc ferrocyanide. If the black-and-white image was not silver or if another bleaching agent or replacing metal is employed the converted image may be another metallic compound containing the replacing metal as one constituent therein and also an element or radical of the bleaching agent as another constituent. Not only should the replacing metal be above the replaced metal in the electromotive series to be operative, but also it should form a Water insoluble compound after the replacement reaction. Zinc ferrocyanide, for instance, is water insoluble and zinc is above silver in the electromotive series. Moreover, silver usually forms the black-and-white image.

It Will be noted that the replacing metal is more chemically active than the replaced metal inasmuch as the higher a metal is in the electromotive series the more chemically active it is. An active metal tends to produce more definite chemical reactions and more stable reaction products than a relatively unreactive metal. Therefore, my novel converted image containing an active metal instead of a relatively inactive metal as does an ordinary bleached image, reacts with color producing reagents in a superior manner and with color producing agents not satisfactorily reactive with an ordinary bleached image. For instance, as pointed out in more detail hereinafter, a diazonium compound is reactive with my novel converted image but is not satisfactorily reactivewith an ordinary bleached image. The reaction product of-this diazonium compound and my converted image may then be colored by suitable azo-dyestuff color producing agents.

I believe that it is preferable to employ as the replacing metal, a metal capable of reacting by means of its unsatisfied residual valence bonds. Zinc in particular is known to possess such residual valence bonds. Therefore, a metal thus characterized and especially zinc, may form a normal chemical compound such as zinc ferrocyanide, which may form my novel converted image as explained above, and thereafter further react due to its unsatisfied partial valences. Thus my converted image is thought to definitely chemically or physically react with color producing agents to produce a stable reacted color forming reaction product. An ordinary bleached image does not appear to react in this manner and does not appear to produce a satisfactory definite chemical reaction with color forming agents and thus does not produce satisfactory color images.

Preparation of the emulsion layer containing the bleached and converted initial bZack-and-white image for the production in that layer of a successive bZack-an'd-white image According to the present invention a plurality of colored images are produced in a single emulsion layer. Each of these colored images is produced from a black-and-white image in said layer. Therefore, it is necessary to provide a satisfactory method of producing a succession of black-and-white images in the single emulsion layer despite the immersion thereof in a bleachingagent for bleaching the initial black-andwhite image as well as immersing the emulsion in my converting solution to convert the initial bleached image to my novel converted image. Normally these bleaching and converting operations would render the emulsion light-insensitive or at least not suited to develop a satisfactory successive black-and-white image. It is a novel feature of the present invention to provide means for resensitizing the emulsion layer containing a bleached converted black-and-white image, that is, to makethat layer capable of producing a successive black-and-white image when exposedand developed at a later step of the process. One operation in thus resensitizing the emulsion layer is accomplished at the same time as the replacement reaction producing my novel converted image from a bleached black-and-white image.

In this replacement reaction a halide of the replacing metal is employed, particularly the bromide. Where these halides and especially the bromides are used, it will be understood that the replaced metal of the bleached image will then form as a reaction product of the replacement reaction, a metallic halide or a metallic bromide. For example, if silver ferrocyanide forms the bleached image and is treated with a solution of zinc bromide as the converting reagent, the bleached image will be converted to a zinc ferrocyanide image and silver bromide will be formed as a reaction product. Such silver halides and bromides are, in the main, lightsensitize and are water insoluble. Therefore, they will be precipitated and distribute themselves throughout the emulsion and thereby form a created deposit of light-sensitive material or will at least form a deposit which may be suitably further treated to form a light-sensitive material. Since, according to the present method, a second or successive black-and-white image is produced in the emulsion after the formation of an initial black-and-white image and the conversion of the latter to my novel converted image having a chemically active metal replaced for a relatively inactive metal in the bleached image, it will be understood that the production of this created deposit for light-sensitive material is important in order that such second or successive image may be satisfactorily produced.

In addition to the deposit of light-sensitive material produced as a reaction product of the replacement reaction in the manner just explained, a residual deposit of the original light-sensitive material will remain in the emulsion. However, these light-sensitive deposits do not necessarily possess the same speed. In fact, normally they do not. Naturally, this condition is highly undesirable inasmuch as a successive black-and-White image produced in the emulsion containing these differently light-sensitive deposits would be spotty, Streaky, and generally defective. According to the present invention these light-sensitive deposits are rendered substantially uniformly light-sensitive by exposing the emulsion without the use of a negative or photographic print. In other words, the emulsion is flashed and completely exposed. It is then developed in a suitable developer and after development will take on theappearance of a fogged print. Th emulsion is next immersed in a desensitizing solution capable of reacting with the developed material deposited in the emulsion to create a deposit of potentially light-sensitive material. This deposit is merely potentially light-sensitive because the desensitizing solution immediately renders it light-in- I sensitive as soon as it is formed. For example,

the developed material after the flash or commaterial is immersed in the desensitizing solution} However, silver bromide does not necessarily have to be that light-sensitive material.

The desensitizing solutions mentioned consist of a solution of an oxidizing agent and therefore an agent capable of giving up electrons. As a result, the gelatin cannot operate to take on electrons from a light-struck image as'it would normally do. Consequently, these desensitizers destroy any latent image which may have been formed in the residual deposit of the original light-sensitive material or in the light-sensitive deposit created at the replacement operation. Several suitable oxidizing agents have been found to operate in this manner. and include halogens, permanganates, perhalates (especially periodates), chromates, dichromates, chromic acid, nitric acid, thiocyanates, and acid halates. It is repeated however, that a desenitizing solution is preferably so selected that it is reactive with the material developed after the flash step to create the suitable light-sensitive mate- The single emulsion layer in which, according to the present invention, a plurality of differently colored images is deposited in registry to form a completed color print contains at the present stage of my process (1) a bleached initial blackand-white image in which the metal forming the black-and-white image has been replaced at the replacement operation by a chemically active metal to form any novel converted image, and (2) a deposit of potentially light-sensitive material consisting of silver halides or some similar material formed after my flash and development operations followed by immersion of the emulsion layer in my desensitizing solution. This deposit is only potentially light-sensitive as my desensitizing solution renders it light-insensitive. It is rendered actually light-sensitive at a later step explained fully hereinafter.

The converted image is next'colored to produce an initial desired colored image and thereafter the emulsion layer containing this colored image is exposed and developed to produce another black-and-white image to be converted into another colored image in the same emulsion layer. The converted image is colored by the following means.

' layer.

assaase The film is washed preferably in water for a length of time suitable to remove any excess reagents particularly any excessdesensitizing solutionwhich may remain in or on the emulsion The washed film is then placed in a solution of a diazonium compound. Any (11 azonium compound may be employed which will react with my novel converted image above described or which will form a chemical addition product therewith. It' is considered impossible to predict whether or not every conceivable diazonium compound will have this characteristic but I have tried a representative number of these compounds and believe that all will act in this manner. However, where zinc is employed as the replacing metal to form the converted image, the reaction appears to be much more marked and satisfactory. The particular diazonium compound selected will depend upon the color of the image to be produced and specific illustrative examples are given hereinafter. It is to be understood, however, that the present invention is not limited to these examples inasmuch as a great variety of diazonium compounds may be employed and a few simple experiments will determine which of these compounds is best suited for a given purpose.

The film is next washed in water for a suitable length of time to remove the excess of the diazonium solution. The temperature of this particular wash should be carefully controlled and should not exceed 10 C.'because the reaction product between the converted image and the diazonium compound apparently tends to break down at higher temperatures. The upper temperature limit which can be safely used varies somewhat with the particular diazonium compound employed and a chemist can readily determine this in any given instance.

The film is then immersed in a solution of a suitable coupling agent. These coupling agents are compounds reactive with the diazonium compounds described above, to produce a water insoluble colored reaction product. In particular, compounds normally referred to in the art as azodyestuff coupling components are recommended. In this case the coupled colored reaction product is known as an azo-dyestuff. Although a wide variety of chemical families may be included as within the scope of the term coupling agent such agents are well known in the art as are methods for producing them; Specific examples of suitable coupling agents are given hereinafter although the present invention' duce widely different colors when used with different diazonium compounds. Moreover, the same chemical reagent may be diazotized and used as a diazonium compound and used in its undiazotized condition as a coupling agent.

It is to be expressly understood that any suitable diazonium compound and coupling agent may be employed and that many such reagents are contemplated. While these diazonium compounds and coupling agents are not completely listed in detail in the present application they are set forth in detail in my copending application, Serial No. 332,070, filed April '27, 1940, to which reference is hereby made for further detailed description of this reaction and compounds for use therein.

The colored image produced by the foregoing steps is now complete in every respect except that the image is not clear due to the presence of reaction products in the emulsion. These reaction products are removed by a so-called clearing operation for-removing such reaction products. However, the silver halide or other potentially light sensitive substance used to produce a successive black-and-white image as explained hereinbeforaremains in the emulsion after this clearing operation. This clearing is accomplished in a solution having a pH value of twelve or more and which preferably also contains a salt in order to prevent any possible dissolving of the colored image. For example, an aqueous solution of KOH and NaOH saturated with NaCl may be used. After removal from the clearing bath the film is immersed in a weak acetic acid solution (such as 5 cc. of glacial acetic acid to 100 cc. of water) to counteract or neutralize the basicity of the emulsion and'to regenerate or reform the acid form of the dyestuff., The film is then washed. This procedure prevents undesired reactions when the film is placed in other diazonium solutions to form a second or successive colored image as explainedhereinafter.

Resensitizing the emulsion layer for the production of a successive black-and-white image At this stage of my process, the emulsion layer contains an initial colored image and a deposit of a potentially light-sensitive material formed as explained hereinbefore, that is, by (l) creating a light-sensitive material such as silver bromide at the replacement reaction also producing my novel converted image, and (2) exposing or flashing this. layer together with a residual deposit of the original light-sensitive material in the emulsion layer, developing the layer, and treating the developed material with a desensitizing agent suited to form a single deposit of a potentially light-sensitive material rendered only potentially light-sensitive because of the action of the desensitizing solution to render it light-insensitive as soon as it is formed.

This deposit is rendered actually light-sensitive by immersing the film in my .resensitizing solution. This solution is made up of an acceptcr, that is, a compound capable of taking up an electron and therefore suitable to react with the light struck, light-sensitive compound to reduce the latter to a visible image. Such acceptors are well known in the art and are reducing agents. Examples of such acceptors are sodium or potassium nitrite, silver nitrite, sulfites, bisulfites. silver sulfite, silver bisulfite, glucose, hydrolyzed gum arabic, fresh gelatin, urea, thiourea, sodium or potassium hydroxide, sodium or potassium carbonate, sodium or potassium bicarbonate, and mixtures thereof. While these resensitizing solutions in and of themselves act as acceptors it is also thought that they perform an additional function. I believe that they also render the gelatin itself active as an acceptor. Gelatin is normally an excellent acceptor but after treatment in the developing, bleaching and converting solutions described hereinbefore this characteristic of the gelatin is lost. Apparently, the present resensitizing solutions serve to restore the gelatin to its normal activity as an acceptor. Therefore, after immersion in the resensitizing solution the film may be washed, if desired, although this washing step does not appear to be necessary.

If it is desired to make the emulsion lightsensitive to a predetermined wave length range, the film may at this point be subjected to the action of suitable agents to accomplish this purpose. Such agents are well known in the art and the film may be rendered particularly light-sensitive to red light, yellow light, or even to blue light although normally the emulsion itself would be sufficiently sensitive to blue light. Various dyes are\ wel1 known in the art for this purpose and the use of any one of them is contemplated herein.

The film at this point is ready for the exposure and development of a successive black-andwhite image in a single emulsion layer. However, it is desirable, although not essential, that the film first be washed or wiped as with a piece of cotton and allowed to dry. It should be understood, however, that the film can be printed wet although, of course, the film speed will be de creased in this event.

Production of a second or successive colored image in the emulsion layer containing the initially formed colored image The film is next re-exposed through another selected color separation negative and-a second .black-and-white image will register. with the colored image already developed. Suitable registering means for achieving this effect are well known in the art. For example, sprocket holes have been found sufiiciently accurate to register the images in the case of motion picture film, and 7 suitable mechanical registering devices may be utilized. After the production of the second black-and-white image it is bleached, treated with a replacing metal, flashed, treated with a desensitizing agent, treated with a diazonium compound and coupling agent, treated with a resensitizing agent and with a panchromatizing agent, if desired, all of which has been described above. As a result, a second colored image will be produced in registry with the initial colored image. It will be understood that the diazonium compound and coupling agents are so selected in treating this second black-and-white image that a desired colored image will be produced. This procedure may be repeated as many times as desired until a selected number of colored images has been produced in the emulsion layer. Normally, however, three images suitably balanced as to color value and intensity will sufiice to produce a natural appearing'complete colored print. It is pointed out, however, that a colored image need not be formed by reacting my converted image with. diazonium compounds and thereafter with coupling agents to produce a colored image. Other suitable color producing means may be employed. For instance, a black-andwhite image bleached with a ferricyanide may be reacted with ferrous or ferric ions to produce a complex iron cyanide blue color producing compound as set forth in a specific embodiment given hereinafter.

Illustrative specific embodiments of the present invention Having thus described my invention, the following specific procedure is givenby way of example but not of limitation. It will be understood that considerable variations may bemade in this procedure in accordance with the foregoing disclosure. In particular, suitable diazo and coupling agents may be selected to provide an image of a desired color. Moreover, the order of the steps is not necessarily that of the specific example given but may be altered in the manner pointed out hereinafter.

Eastman positive nitrate film, bearing emulsion number K-1301, having a single coating of emulsion, is used as a starting material. This film is treated according to the following steps which,

for purposes of convenience. are presented innumbered paragraphs.

(1) Select the magenta representing color separation negative, that is, thelnegative suitable for use in making a magenta colored image. Use this negative to expose a black-and-white positive image.

(2) Develop the imagethus exposed. A suitable developer is Eastman Developer 13-11. A developing time of approximately 4 minutes at about 18 C. is used. The film is washed for about minute after treatment in the developing solution and is then placed in a conventional short stop bath, such as a solution of weak acetic acid, for about 1 minute and is thereafter washed for about 3 minutes.

(3) Place the print in a bleaching bath of potassium ferricyanide. The ferricyanide solution is an aqueous solution containing 10 grams of ferricyanide to each 100 cc. of water. This solution may be rendered basic by the introduction of approximately 2 grams of solid sodium hydroxide and/or about grams of sodium carbonate per 100 cc. The print is left in this bleaching bath until it is substantially completely bleached which may be noted visibly and which will take approximately 5 minutes.

(4) Immerse the film in a suitable hardening bath. The following solution is used:

Formaldehyde (40% aqueous solution) cc NazCOs (40% aqueous solution) cc 5 Water to make "liter" 1 The film is left in the hardened solution for a suitable length of time. Approximately 5 minutes has been found sufilcient.

(5) The film is then washed to remove the excess of the ferricyanide and hardener. Approximately a 5 minute wash in gently running cool water (about 18 C.) is used.

(6) The film is then placed in a solution of zinc bromide. An approximately 10% aqueous solution of zinc bromide is employed, that is, approximately 10 grams of zinc bromide to each 100 cc. of water. Approximately 1 cc. of acetic acid is added per 100 cc. of water. The film is left in the zinc, bromide solution for approximately 5 minutes. The film is preferably washed after this immersion.

('7) The film is then flashed, that is, it is exposed to light without the use of a negative. This exposure may be any suitable length of time suitable to thoroughly expose all the light-sensitive material in the emulsion. After this exposure the film is suitably developed in a developer, such as Eastman D-ll, and is subjected to a short stop and wash in the manner explained in the foregoing steps. At this point the film will have a substantially uniformly dark appearance resembling a developed fogged film.

(8) The fiashed and developed print is next immersed in a solution of bromine water. The concentration of this solution should be about 25% to 50% solution of sati'trated bromine water at 20 C., that is, approximately 25 to 50 cc. of a saturated (at 20 C.) aqueous solution to each 100 cc. of water. The film is left in the bromine water until the developed material is converted to a bromide which may, of course, be noted visibly by the disappearance of the black color of the film. This conversion will usually take place in'less than 5 minutes.

(9) After this conversion is complete, the film is washed in order to remove the excess bromine. Agently flowing water wash at approximately 18 C. is used and a complete washing should take place in approximately 3 to 5 minutes.

(10) The film is next immersed in a solution of alpha naphthyl diazonium sulfate. Approximately .2 molar solution of this diazonium com-'- pound is used and is bufie'red with approximately 10 grams of sodium acetate for each 250 cc. of the solution. The film is left in this diazonium solution'for approximately 5minutes.

(11) After treatment in the diazonium solution the film is very carefully washed. This wash should be relatively rapidly flowing water at not more than 18 C. and should be at least 5 minutes in duration.

(12) The film is next placed in a coupling solution. Abasic aqueous solution of beta naphthol is employed. A concentration of approximately 5 grams per 100 cc. is used with about 1 gram of solid sodium hydroxide added. The film is left in this coupling solution until the reaction is completed, which may be noted visibly by the magenta appearance of the image. While this reaction takes place in approximately 1 minute, the film is left in the solution for about 5 minutes.

13) The film is next placed in a clearing solu-' tion consisting of a 2%. queous solution of sodium hydroxide saturated with sodium chloride. The film is left in this solution until it clears, which takes place in about 5 minutes.

(14) The film is next carefully washed for approximately 5 minutes. in gently flowing cool water.

(15) After this wash, the film is immersed in a resensitizing solution consisting of a 5% aqueous solution of sodium sulfite. The film is left in this solution for approximately 5 minutes and is then removed from the solution, is wiped with a piece of cotton, and is allowed to dry thoroughly. This drying step will take about an hour if the film is hung up in a normal darkroom.

. (16) The color separation negative representing yellow is now selected, that is, the negative which is suitable for use in making the yellow image. This negative is carefully registered on the magenta image produced by the foregoing steps. This registration may be accomplished by means of sprocket holes in the film or by any After step No. and is treated with zinc bromide in the manner explained in step No. 6. It will be noted that a hardening solution, such as the one explained in step No. 4, is not utilized at this point.

, (19) The film is next treated with a bromine solution similar to the treatment explained in step No. 8. However, the concentration of the bromine need not be as great as there set forth, and can be about cc. of saturated bromine water to each 100 cc. of solution. The film is left in this bromine water for about 5 minutes and is washed thereafter. This wash is preferably for about 5 minutes but a 2 to 3 minute wash will suffice.

(20) The film is then immersed in a solution of para-nitrodiazonium sulfate. This solution is approximately .2 molar and is buffered with 10 grams of sodium acetate for each 250 cc. of solution. The film is leftin this solution for about 5 minutes and is carefully washed in the manner explained in step No. 11.

(21) After this wash, the film is immersed in a coupler suitable to produce a yellow color. An aqueous solution of alpha naphthol, approximately 1 gram for each 100 ccQof solution, is employed. This solution is rendered slightly basic by the addition of about .5 of a gram of solid sodium carbonate. The film is left in this solution until the coupling action is completed which may be noted visibly and takes place in about 2 to 5 minutes.

(22) After coupling, the film is washed for about 1 minute and is placed in a basic solution as outlined in step No. 13 for about 2 minutes. The color of the image will change from yellow to a deep purple and the film is left in this solution until this reaction takes place, which will be in about 2 minutes. Preferably, the film should not be left in this solution longer. After treatment in the basic solution, the film is again washed for approximately 1 minute and is immersed in a weak acetic acid solution for about 3 minutes. The film will become yellow when immersed in this acetic acid solution.

(23) The film is then treated in a resensitizing solution and dried in the manner outlined in step No. 15. v

(24) The blue representing color separation negative is now selected and is used to print the image to be converted to blue. This negative is registered on the combined yellow and red images now in the emulsion in the manner indicated in step No. 16.

(25) After printing, the film is developed in the manner set forth in step No. 2 and is bleached in the Way set forth in step No. 3.

(26) After the bleaching, the film is carefully washed in the way set forth in step No. 5 and is oxidized by immersion in a solution of nitric acid. An aqueous solution containing 25% to by weight of concentrated nitric acid is employed. The print is left in this solution until oxidation is completed, which takes place in about 1 minute.

(27) After oxidation is completed, the film is thoroughly washed and is placed in a blue producing bath made up as follows:

Sodium thiosulfate gms 2 Acid mixture cc 20 Ferrous sulfate solution cc. 30 Water (at approximately 18 C.) to

make cc 150 The ferrous sulfate solution referred to is made up as follows:

Sulfuric acid (concentrated (1.8 gms.)

The film is left in this solution until the blue image is completed, which will take about 5 minutes.

(28) The film is then treated with a conventional hypo solution, is suitably washed and dried, and is completed.

Some alternative procedures embodying the present invention It should be expressly understood that the order of the ste given in the foregoing example is not the only order which can be followed in practicing the present invention. In particular, the first black-and-White positive image need not be completely converted into a colored image prior to the printing and development of the succeeding black-and-white image. Provided that the first black-and-white image isv developed, bleached and treated with the replacing metal, such as zinc as outlined in step No. 6, the second image may be thereafter printed anii developed. After the printing and development of the second image, the first image may be treated to complete its conversion to color. After this treatment the second image may then .be bleached and treated with the replacing metaL' At this point the second image may be converted to color or the third image,

may be printed and developed prior to the completion of the color formation of the second image.

The desensitizing operation, such for instance as step No. 8, may be inserted at any suitable point after treatment of the bleached image and the resensitizing step, such for instance as step No. 15, may be inserted at any suitable point after the desensitizing step. However, the resensitizing step does not have to follow directly after the desensitizing step. The

hardening step may be inserted at any suitable point and the clearing step may be inserted at any point after the development of the colored images. Moreover, many of the wash steps referred to may be eliminated provided that a thorough washing is accomplished at some time after the ferricyanide. conversion step and prior to the treatment with the replacing metal, such as zinc, and provided further that a thorough washing is also accomplished after the diazo step, such as steps No. 10 or No. 20 and prior to the coupling step, such as steps No. 12 and No. 21. In addition, a wash step may be added after the resensitizing step if desired, although it is not necessary. Furthermore, the flash stepas outlined in step No. '7 may be inserted at any suitable point prior to the desensitizing step.

While any suitable procedure in accordance with the foregoing disclosure may be used in ing alternative procedure is given by way of example but not of limitation. In this alternative procedure, steps Nos.-1 through 6 of the' foregoing example are followed. At this point the image to be converted into yellow is printed and developed in the manner outlined in steps Nos. 16 and 17, but is not bleached. Thereafter the color formation for the magenta or initial image is completed by following steps Nos. 7 through 15. The developed black-and-white image to be converted into yellow is then bleached and treated with the zinc in the man-' color is completed .by bleaching the .blue representing black-and-white image as explained in step No. 24 and then following steps Nos. 25 through 28.

While only one specific alternative procedure is given herein, it will be appreciated that other alternative procedures may readily be devised in view of the present disclosure.

In addition to altering the order of the steps in the present process, certain of these steps may I carrying out the present invention, the followance to the eye of the desired shade of orange. Similarly other shades of colors are produced. Not only does a color print of this character produce a superior and natural appearing color print, but also produces better results on projection because distortion, loss of definition, out-offocus images, and other defects resultant from projecting a print consisting of superimposed layers having separate images are eliminated.

I claim:

l. A photographic process for producing a plurality of images in a single emulsion layer having an initially light-sensitive sliver compound, comprising an exposure 01' the layer, a development of a reduced silver image therein, the said steps being so controlled as to leave aresiduai deposit of the initially light-sensitive silver compound in the emulsion, bleaching the image to a silver ferrocyanide image, reacting the bleached image with zinc bromide thereby producing a reaction product image consisting of zinc ferrocyanlde and generating silver bromide, immersing the emulsion layer in a solution of an oxidizing agent for desensitizing it, reacting the zincferrocyanide image with a diazonium compound followed by reacting therewith a coupling agent reactive with the diazonium compound to produce a colored reaction product, immersing the layer in a solution of an acceptor'for rendering the emulsion uniformly light-sensitive, and exposing and developing a successive black-and-white image -in be combined. In particular, the hardener solution may be added to other suitable solutions such as the ferricyanide bleaching bath. It is considered evident that a skilled chemist can readily determine which of these baths the hardener solution may be added to without causing undesired chemical reaction's. Moreover, the zinc bromide bath may be combined with the diazo bath if desired. This combination may be ac complished by simply mixing the two baths together and treating film therein in place of treating it in the two separate baths. This procedure is not particularly recommended, however. Moreover, the sodium hydroxide clearing bath may be added to the coupling bath so that the color is formed and also cleared in a single solution. If it is desired to make but a single colored image in the emulsion layer, the hypo solution may also be added to this combined coupler and clearing solution.

Character of the completed color print In view of the foregoing, it will be understood that according to the present invention a plurality of color images is deposited in registry in a single emulsion layer to form a completed color print. Unlike prior color processes, these images are not superimposed on one another in separate layers of emulsion or in separate prints assembled on a common carrying means. On the contrary, these images are deposited on a common plane. Colored grains or minute colored parts of the gelatin once forming an image of one color are deposited substantially side-by-side in a relativeiy thin emulsion layer with those initially forming an image of another color. In the completed color print these grains are so placed that a natural color print results. For instance, the pure red portions of the scene photographed are represented in the print by red particles only while the orange portions thereof are represented by substantially coplanar grains of red and also of Yellow in proportions suited to give an appearthe emulsion layer so sensitized and coloring said image.

2. In a photographic process for producing a plurality of colored images in a single emulsion layer, the steps of developing a reduced silver image in the layer while leaving a deposit of silver bromide therein, bleaching the silver image to a silver ferrocyanide image, reacting the latter in a bath containing zinc bromide thereby forming an additional deposit of silver bromide in the emulsion layer, immersing the said layer in a solution of an acceptor thereby. rendering it uniformly light-sensitive, and reacting thereacted bleached image with a diazonium compound followed by an azo-dyestufi coupling agent to produce a colored image.

3. A photographic process for producing a plurality of images in a single initially light sensitive emulsion layer containing a silver halide, comprising an exposure of the layer, a development of a reduced silver image therein, said steps being so controlled as to leave a residual deposit of the initially light sensitive'silver halide in the emulsion, bleaching the image to a silver ferrocyanide image, reacting the bleached image with the zinchalide corresponding to the aforesaid silver halide thereby regenerating the light sensitive silver halide, again exposing the emulsion layer and reducing to metallic silver the silver in said residual deposit and also in said regenerated material, reacting said metallic silver with bromine to provide a deposit of silver bromide in the emulsion, reacting the aforesaid reacted bleached image with a diazonium compound followed by reacting it with a coupling agent reactive with the diazonium compound, immersing the emulsion layer in an acceptor for rendering the emulsion substantially uniformly light sensitive, and developing a successive image in the emulsion layer so sensitized.

4. A photographic process for producing a pin. rality of images in a single emulsion layer having an initially light sensitive silver compound, comprising an exposure of the layer, a development of a silver image therein, said steps being so controlled as to leave a residual deposit of the initially light sensitive silver compound in the emulsion, bleaching the image to a silver ferrocyanide image, reacting the bleached image with a zinc halide thereby producing a reaction product image consisting of zinc ferrocyanide and producing a silver halide, immersing the emulsion layer in a solution of an oxidizing agent for desensitizing it, reacting the zinc ferrocyanide image with a diazonium compound followed by reacting therewith a coupling agent reactive with the diazonium compound to produce a colored reaction product, immersing the layer in a solution of an acceptor for rendering the emulsion substantially uniformly light sensitive, and exposing and developing a successive black-andwhite image in the emulsion layer so sensitized and coloring said image.

5. A photographic process for producing a plurality of images in a single emulsion layer having an initially light sensitive silver compound, comprising an exposure of the layer, a. development of a reduced silver image therein, said steps being so controlled as to leave a residual deposit of the initially light sensitive silver compound in the emulsion, reacting the silver image with an iron cyanide to form an insoluble silver iron cy anide image, reacting the last said image with a zinc halide thereby producing a reaction product image consisting of an insoluble zinc iron cyanide and producing a silver halide, immersing the emulsion layer in a solution of an oxidizing agent for desensitizing it, and exposing and developing a successive black-and-white image in the emulsion layer so sensitized and coloring said image.

6. A photographic process for producing a plurality of images in a single emulsion layer having an initially light sensitive silver compound, comprising an exposure of the layer, a development of a reduced silver image therein, bleaching the image to a silver ferrocyanide image, reacting the bleached image with zinc bromide thereby providing a reaction product image consisting of zinc ferrocyanide and producing silver bromide, immersing the emulsion layer in a solution of an oxidizing agent for desensitizing it, reacting the zinc ferrocyanide image with a diazonium compound followed by reacting therewith a coupling agent reactive with a diazonium compound to produce a colored reaction product, immersing the layer in a solution of an acceptor for rendering the emulsion substantially uniformly light sensitive, and exposing and developing a successive black-and-white image in the emulsion layer so sensitized and coloring said image.

'7. A photographic process for producing a plurality of images in a single emulsion layer having an initially light sensitive silver compound, comprising an exposure of the layer, a development of a silver image therein, reacting said image with a complex iron cyanide to form an insoluble silver complex iron cyanide image, reacting the last said image with a zinc halide thereby producing an insoluble zinc complex iron cyanide image and producing a silver halide, immersing the emulsion layer in a solution of an oxidizing agent for desensitizing it, reacting the zinc complex cyanide image with a diazonium compound followed by reacting therewith a coupling agent reactive with a diazonium compound to produce a colored white image in the emulsion layer so sensitized and coloring said image.

8. In a photographic process for producing a plurality of colored images in a single emulsion layer, the stepsof developing a silver image in the layer while leaving a deposit of a light sensitive silver halide therein, reacting the silver image with a complex iron cyanide to form an insoluble silver complex iron cyanide image, reacting the latter in a bath containing a zinc halide thereby forming a deposit of silver halide in the emulsion layer, immersing said layer in a solution of an acceptor thereby rendering it substantially uniformly light sensitive, and reacting the reacted bleached image with a diazonium compound followed by an azo dye-stuff coupling agent to produce a colored image.

' 9. In a photographic process for producing a plurality of colored images in a single emulsion layer, the steps of developing a reduced silver image in the layer while leaving a deposit of silver halide therein, bleaching the silver image to a silver ferrocyanide image, reacting the latter in a bath containing a chemically active halide of a metal above silver in the electromotive series, thereby forming an additional deposit of silver halide in the emulsion layer, immersing the said layer in a solution of an acceptor thereby rendering it uniformly light-sensitive, and reacting the reacted bleached image with a diazonium compound followed by an azo-dyestufi coupling agent to produce a colored image.

10. A photographic process for producing a plurality of images in a single initially light sensitive emulsion layer containing a silver halide, comprising an exposure of the layer, a development of a reduced silver image therein, said steps being so controlled as to leave a residual deposit of the initially light sensitive silver halide in the emulsion, bleaching the image to a silver ferrocyanide image, reacting the bleached image with a chemically active halide of a metal above silver in the electromotive series corresponding to the halide of the aforesaid silver halide, thereby regenerating the light sensitive silver halide, again exposing the emulsion layer and reducing to metallic silver the silver in said residual ,deposit and also in said regenerated material, reacting said metallic silver with bromine to provide a deposit of silver bromide in the emulsion, reacting the aforesaid reacted bleached image with a diazonium compound followed by reacting it with a coupling agent reactive with the diazonium compound, immersing the emulsion layer in an acceptor for rendering the emulsion substantially uniformly light sensitive, and developing a successive image in the emulsion layer so sensitized.

11. In a photographic process for producing a plurality of colored images in a single emulsion layer, the steps of developing a silver image in the layer while leaving a deposit of a light sensitive silver halide therein, reacting the silver image with a complex iron cyanide to form an insoluble silver complex iron cyanide image, reacting the latter in a bath-containing a chemically active halideof a metal above silver in the electromotive series, thereby forming a deposit of silver halide in the emulsion layer, immersing said layer in a solution of an acceptor thereby rendering it substantially uniformly light sensitive, and reacting the reacted bleached image with a diazonium compound followed by an azodyestufl' coupling agent to produce a colored 

